This invention relates to electronic test systems, and more particularly to testers for memory modules including SIMMs and DIMMs.
Most personal computers (PCs) use DRAM memory chips mounted on small, removable memory modules. Originally produced as single-inline memory modules (SIMMs) with memory organized into sizes such as 256Kxc3x979 and 1Mxc3x979, more recent memory modules use wider I/O. Thus 4Mxc3x9732 modules are commonplace today. Additional I/O is facilitated by using dual-inline memory modules (DIMMs), such as 168-pin modules.
Huge demand for memory modules has resulted in an extremely crowded and competitive industry that is very cost sensitive. Testing costs are significant, especially for higher-density modules that have more memory locations that must be tested. Specialized, high-speed electronic test equipment is expensive, and the greater number of memory cells on high-speed memory modules increases the time spent on the tester, increasing costs.
Handlers for integrated circuits (ICs) have been used for many years in the semiconductor industry. These handlers accept a stack of IC chips that are fed, one at a time, to the tester. Once tested, the IC is sorted into a xe2x80x9cbinxe2x80x9d, another stack of IC chips that have either passed or failed the test. ICs from good bins are packaged for sale, while ICs from bad bins are thrown out. Bins can be set up for different types of failures (open circuit, short circuit, functional failures, out-of-spec parameters. etc.) and statistics kept for analysis by engineers.
More recently, handlers have been made for memory modules. U.S. Pat. No. 5,704,489 by Smith, describes in detail a xe2x80x9cSIMM/DIMM Board Handlerxe2x80x9d such as those in use today. FIG. 1 shows a SIMM handler connected to a high-speed electronic tester. Handler 10 is of the type described by Smith. Memory modules 18 to be tested are loaded into the top of handler 18 in the input stack. Memory modules 18 as shown have DRAM chips surface-mounted to both sides of the substrate, as is well-known in the art. These modules 18 drop down, one-by-one, into testing area. Module-under test MUT 20 is next to be tested. Arm 26 pushes MUT 20 laterally until it makes contact with contactor pins 16 that clamp down on xe2x80x9cleadlessxe2x80x9d connector pads formed on the substrate of MUT 20.
Pins 16 thus make electrical contact with the 168 leadless contact pads of memory-module MUT 20. Contactor pins 16 are also connected to test head 14, which makes connection to tester 12. Tester 12 executes parametric and functional test programs that determine when MUT 20 falls within specified A.C. and D.C. parameters, and whether all memory bit locations can have both a zero and a one written and read back. Shorts between adjacent memory bits cable detected by performing tests using various test patterns, such as walking-ones, walking zeros, and checkerboard.
Tester 12 can cost from ten-thousand to millions of dollars. Cost can be reduced if a less-expensive tester replaces tester 12. Since most memory modules are intended for installation on PCs, some manufacturers test memory modules simply by plugging them into SIMM or DIMM sockets on PC motherboards. A test program is then executed on the PC, testing the inserted module. Since PCs cost only about a thousand dollars, tester 12 and handler 10 of FIG. 1 are replaced by a low-cost PC. Equipment costs are thus reduced by a factor of a hundred.
FIG. 2 shows a PC motherboard being used to manually test memory modules. Substrate 30 is a glass-epoxy motherboard having multiple layers of patterned conductor traces sandwiched between insulating layers, as is well-known in the art. Components 42, 44 are mounted on the top side of substrate 30, such as by wave-soldering. Components 42, 44 include ICs such as a microprocessor, logic chips, buffers, and peripheral controllers. Components 42, 44 may be directly mounted onto the top surface, or may have pins that are fitted into holes in the substrate. These pins are then soldered to the backside of substrate 30. Sockets for expansion cards 46 are also mounted onto the top or component side of substrate 30, while their pins are placed through holes in substrate 30 and soldered to the back side of substrate 30. Some of components 42, 44 may also be mounted in sockets.
Memory modules 36 are SIMM or DIMM modules that fit into SIMM/DIMM sockets 38. SIMM/DIMM sockets 38 (hereinafter SIMM sockets 38) have metal pins that fit through holes in substrate 30. These pins are soldered to solder-side 34 of substrate 30 to rigidly attach SIMM sockets to the PC motherboard. Both electrical connection and mechanical support are provided by SIMM sockets 38.
While using PC motherboards for testing memory modules greatly reduces equipment costs, labor costs are increased. Memory modules must be inserted and removed manually. Manual insertion and removal of memory modules is slow and labor-intensive. It also wears the leadless contact pads on the modules, which can give the appearance that the modules is used rather than new.
While it is desirable to use a SIMM/DIMM handler to insert and remove memory modules for test, expansion cards 46 and cables 48 can block access to SIMM socket 38. Thus the crowded area around SIMM socket 38 on the PC motherboard prevents putting a handler in close proximity to the SIMM socket. A person must reach in with his hands and manually insert SIMM 20 into SIMM socket 38.
Connecting a handler to SIMM socket 38 using a long cable is possible, since the long cable allows the handler to be farther away from the crowded PC motherboard. However, the long cable is not desirable since it adds significant loading to the PC""s memory bus. This loading slows the memory operation down, resulting in test failures for good memory modules. Interference can also be inserted into the memory bus by the long cable.
What is desired is a low-cost test apparatus for testing memory modules. It is desired to reduce testing costs by eliminating the expensive electronic tester. It is desired to use a PC motherboard or other target-system board to test the memory modules. It is further desired to use a SIMM/DIMM handler to automatically insert and remove memory modules that are tested by a PC motherboard. It is desired to connect the handler to a PC motherboard without a long cable so that the loading on the PC""s memory bus is minimized, allowing full-speed testing.
An automated test apparatus tests high-speed memory modules using a memory-module handler. A target-system motherboard has components including a microprocessor, memory, and expansion-bus connectors mounted on a component-side of the target-system motherboard. The memory includes memory modules inserted into memory-module sockets mounted on the component-side.
A handler adaptor board has adaptor pins protruding out a first side and has connector sockets mounted on a second side opposite the first side. At least one of the memory-module sockets has been removed. The adaptor pins connect to the target-system motherboard on a solder-side of the target-system motherboard immediately opposite a location where the at least one memory-module sockets have been removed.
The connector sockets on the handler adaptor board connect to the memory-module handler. They connect signals from a memory module under test in the memory-module handler to a memory bus on the target-system motherboard. Thus the memory module under test in the memory-module handler is electrically connected to the target-system motherboard.
In further aspects of the invention a handler controller card is inserted into one of the expansion-bus connectors. The handler controller card communicates with the memory-module handler when the memory-module under test in the memory-module handler is tested by the target-system motherboard. Thus the memory-module handler is controlled by the target-system motherboard.
In still further aspects the handler controller card has a sorting means that is coupled to the memory-module handler through a handler cable. It sends a sort signal to the memory-module handler at a completion of tests of the memory-module under test. The sort signal instructs the memory-module handler to sort the memory-module under test into either a good bin or functional memory modules or into a bad bin of faulty memory modules. A ready signal from the memory-module handler indicates when the memory-module handler has moved a new memory-module to a test position.
In other aspects the handler controller card has a flash memory means that stores a test program. The test program tests the memory-module under test in the memory-module handler. The test program is executed by the microprocessor on the target-system motherboard.
A power control means is coupled to the handler adaptor board thorough a power cable. It disconnects power to the memory-module under test when the memory-module handler is moving another memory module to a test position. Thus power to the memory-module under test is disconnected when tests of the memory-module under test is completed.